I've wondered a lot about why e-mail isn't used more as a backend for different services. But as far as I can tell, messaging products proliferate because their creators want to create profitable products rather than distributed protocols.<p>E-mail is a pretty good group of protocols for distributing arbitrary messages between different locations on the Internet. It's easy to imagine how all sorts of messaging and social network products could be implemented as a specialized e-mail client with a good user experience. Their forms might be slightly different than they have now, but they'd serve approximately the same consumer purpose.<p>For example, you could build a social networking "client" with e-mail as a backend. Status updates, photos, etc. would be distributed to all your contacts via email, and the client would produce a "timeline" based on the data in its mailbox, without ever showing the user the original messages.<p>But you give up a lot of control that way, and it's harder to monetize. What developers want (and users too, to be honest) is a centralized service that they can control, mine data with, and sell products or show ads. A distributed protocol, while in some ways more powerful (and less dependent on a fallible central authority!), doesn't achieve the real business aims.